In the International Study of Kidney Disease in Children 24 participating clinics in 12 countries throughout the world are conducting clinical surveys and therapeutic trials on major kidney diseases in children. Trials in progress include (1) the effect of cyclophosphamide in patients with (a) focal segmental sclerosis and (b) anaphylactoid purpura and (2) the effect of prednisone in patients with (a) minimal change nephrotic syndrome and (b) membranoproliferative glomerulonephritis. Protocols have been developed for therapeutic trials of (1) imuran in patients with diffuse, proliferative lupus nephritis and (2) streptokinase in patients with hemolytic-uremic syndrome. Clinical surveys are being conducted on the natural history of patients with (1) the nephrotic syndrome: (2) recurrent hematuria; (3) familial nephritis; and (4) membranous nephropathy. An index of all patients with kidney disease seen in the participating clinics has been established to define populations available for other studies.